The invention relates to a process for scrubbing out gaseous components from gaseous mixtures with a physical solvent which is regenerated by expansion and stripping and in particular wherein the gaseous fraction from the stripping step is discharged and the resultant regenerated solvent is recycled to the scrubbing step.
It is old to utilize physical solvents for the purification of gases, e.g., synthesis raw gases containing CO.sub.2, COS, and H.sub.2 S, or of cracked gases of acetylene. Since the absorption capacity of the physical solvents, such as methanol, for example, for the gaseous components to be scrubbed out increases with decreasing temperature, these scrubbing operations are conducted at as low a temperature as economically and technically feasible. In this connection, with the use of methanol, the scrubbing temperatures are considerably below 0.degree. C., e.g., generally at about -5 to -65.degree. C. Regeneration of the physical solvent loaded with the scrubbed-out gaseous components is conventionally conducted in a combination of pressure reduction and/or stripping and/or thermal regeneration steps. In this regeneration process, the absorbed gaseous components are released and the regenerated solvent is recycled into the scrubbing step.
Among the thus-released gases, CO.sub.2 and N.sub.2, the latter is generally utilized as the stripping gas, and can be discharged, for example, directly into the atmosphere. However, this gaseous fraction still contains in all instances a proportion of concomitantly driven-out solvent vapors. This solvent content of the gases leaving the scrubbing step is dependent on the temperature and pressure at which the gases are separated from the liquid solvent. According to presently enforced regulations to prevent atmospheric pollution, the expulsion of solvent vapors must not exceed a content dependent on the respective type of solvent. For this reason, it has been suggested to subject the gases to be discharged into the atmosphere to an additional purifying process, for example a water scrub or an adsorption procedure, in order to lower the solvent content in the gas. However, separation of the solvent from water, or regeneration of the adsorber requires a considerable expenditure in energy and apparatus.